New energy vehicles are widely promoted in the country and even in the world. However, in order to completely replace fuel vehicles, there are many areas for improvement. For example, there are a few problems such as low travelling mileages of vehicles, high cost of battery packs, reliability of battery packs and the like, which need to be further solved. In view of these problems, higher requirements have been proposed for a power battery as a core part of an electric vehicle, such as higher energy density, lower cost and so on.
For the power battery, in order to overcome the problem of overcharging, a conventional solution in the industry is to cut off the path of charging and discharging of the power battery before the failure of an electrode assembly, so as to prevent the power battery from continuing to be charged and thus ensure the safety of the power battery. A common structure is that a through hole is provided in a cap plate, one end of a conductive sheet is electrically connected with the electrode assembly, and the other end of the conductive sheet is inserted into the through hole and electrically connected with a terminal board through a deformable sheet provided on the terminal board. In this structure, in order to fix the conductive sheet, a part of the conductive sheet near the electrode assembly needs to go beyond an outer edge of the through hole, and the part of the conductive sheet beyond the outer edge of the through hole needs to be wrapped by insulating plastic so as to be fixed with the insulating plastic. Then the insulating plastic is fixed under the cap plate so that the conductive sheet is fixed to the cap plate.
However, with the above described structure, since the insulating plastic is located under the cap plate and the conductive sheet is only fixed by the insulating plastic, the insulating plastic may be loose under the action of gravity of the conductive sheet and the insulating plastic during long-term use and as a result, the reliability of the connection between the conductive sheet and the cap plate may decrease. Meanwhile, the insulating plastic for wrapping the conductive sheet may occupy an internal space of a case of the power battery, thereby increasing the thickness of a cap assembly and affecting the energy density of the power battery.
There is another structure in which the conductive sheet is directly welded onto the cap plate, one end of the conductive sheet is electrically connected with the electrode assembly, and the other end of the conductive sheet is electrically connected with the terminal board through the deformable sheet provided on the terminal board. With this structure, since the conductive sheet is directly connected with the cap plate, the on-resistance between the conductive sheet and the cap plate is very small. In a nail penetration test, when a nail pierces the case (the cap plate is connected with the case) and the electrode assembly, a large external short-circuit current will be generated, possibly causing sparking which may trigger fire or other security problems.